Beads can control material flow as a punch forms a workpiece, such as a blank of material. A typical bead includes a male portion on a first die, and a female portion on a second die.
During forming, the bead holds some areas of the workpiece between the male and female portions. After the punch forms a desired shape in the workpiece, extra material is removed from the desired shape. The extra material can include the areas held between the male and female portions of the bead after forming the desired shape.
The bead can provide a varied amount of resistance to material flow based on, among other things, the material composition of the workpiece and whether lubricants are used during the forming. That is, a bead that can substantially prevent flow of a steel workpiece during forming may be unable to prevent flow of an aluminum workpiece, especially if the aluminum workpiece is lubricated. Example beads include draw beads, which permit some material flow during forming, and lock beads, which substantially prevent material flow.
If a single bead does not provide a desired resistance to material flow, some material forming processes include more than one bead between an outer edge of the material and an area of the material contacting the punch. Holding the material with more than one bead during forming increases resistance to material flow, but can also increase a size of the workpiece required to form the desired shape. If the size of the workpiece increases, there is more extra material after forming the desired shape.